The present invention generally relates to the treatment of soils for the purpose of enhancing agricultural yields. More particularly, the invention pertains to methods for preventing the escape of fumigants that are injected into the soil prior to planting. Fumigants that function as herbicides, insecticides, fungicides or nematicides are necessarily toxic in nature and it is therefore most desirable to minimize their release to the atmosphere.
Various fumigant formulations are available for the eradication or reduction of specific organism populations that are harmful to certain crops. Chloropicrin and 1,3-Dichloropropene are examples of active ingredients that are used in such formulations which may further include a variety of additives that serve to modify the chemical and physical characteristics of the composition as well as its toxicological effect.
Injection of the fumigant into the soil is typically accomplished by the use of tractor mounted chisels and/or plows. The depth of injection and the injection rate is carefully controlled so as to maximize the effect of a particular fumigant on the targeted pest or disease. Due to the volatile nature of such compositions, they tend to freely disperse through the soil as well as transfer to the atmosphere. It is therefore desirable to trap the gases in the soil in order to not only extend the time period in which the organisms are exposed but to prevent the concentrated release of the fumigant into the atmosphere. Extended residence time within the soil allows the fumigant to be absorbed, decomposed or degraded while the escape of some of the fumigant is distributed over a longer period of time.
A number of different approaches have been suggested and actually employed in an effort to trap fumigant in the soil. To date, the most widely used approach involves covering a treated field with polyethylene sheeting immediately after injection. A number of substantial disadvantages are, however, associated with such method. The material cost is significant and the deployment of acres of sheeting requires a fairly labor intensive effort. This would include the steps that must be taken to ensure that a proper seal is achieved between adjacent panels of sheeting as well as about the periphery of the covered area. The sheeting must additionally be sufficiently taut and anchored to prevent wind damage. After the treatment is complete, the sheeting must be removed and disposed of which adds substantially to the costs. Finally, it has been discovered that the polyethylene sheeting is in fact not particularly impermeable to certain fumigants which of course severely limits its efficacy.
More recently, the use of various film forming compositions have been suggested wherein a liquid composition is applied to the soil after injection of the fumigant. The material polymerizes in situ to form a film and may be formulated to decompose or degrade after a preselected period of time has elapsed or upon extended exposure to the sun's ultraviolet radiation. The material is easily tilled under prior to planting whereby it serves as a nutrient in the soil. Shortcomings inherent in these heretofore suggested systems include their limited ability to form a continuous, impermeable barrier at economically feasible rates of application.
A need continues to exist for an inexpensive, easily applied and environmentally compatible system that prevents or reduces the escape of fumigant from treated soils.